Various types of wet film applicators, in particular, those used for testing paints, are known from the prior art. For the correct determination of some special properties of coatings such as color, transparency, luster, strength, resistance to weathering and chemical factors, etc., it is necessary to ensure that the test coatings applied in sequential runs would have the same preset thickness. In addition, it is desired that the applicator device would be adjustable so as to obtain the films of the desired thickness from various substances having varied physical properties.
One wet film applicator known from the prior art comprises a pair of wedge-shaped elements, which are parallel to each other and bear a transverse plane blade forming the coating. A gap between the bottom edge of the blade and the base plane (substrate) determines the thickness of the applied coating. The thickness of this gap is varied when the blade is moved along the wedge-shaped elements. Once the required gap thickness is set, the mutual arrangement of parts in the device is fixed. The blade is oriented perpendicularly to the direction of application and forms a film of desired thickness when the applicator is moved relative to the substrate surface. This device is quite universal and provides the level of accuracy that is sufficient for the formation of usual paint, lacquer, and other wet film coatings. In the clamping mechanism, the tightening screws directly presses against the blade which imparts a twisting motion to the blade However, neither this accuracy of this device nor (which is more important) the mode of device interaction with the applied liquid are sufficient for the formation of high-quality optically anisotropic films and coatings, especially such as are employed in modern multilayer interference devices.
Thin films with anisotropic optical properties, which are formed using liquid-crystalline solutions of organic dyes, are now widely used in science and technology. The molecules of these organic compounds have planar configuration and form orientation-ordered supramolecular complexes in solution. When a solution of these organic molecules is applied onto a substrate surface in the presence of an external orienting action (alignment), the resulting coating acquires a macroscopic orientation (optical anisotropy), which is not only retained in the course of subsequent drying but can even increase as a result of crystallization. The polarization axis is oriented along the direction of the aligning action, which coincides with the direction of application of the coating. Specific structural features of such optical films determine the need for developing special coating devices capable of forming precise thin layers with the required molecular orientation.
There are various known methods for the formation of optically anisotropic films and, accordingly, various devices which implement these methods. For example, liquid-crystalline solutions can be applied using a drawing plate or a wiper (squeegee), which can be of a blade (sheet) or cylinder type. The application of a liquid-crystalline solution onto a substrate surface can be performed simultaneously with the orientation of supramolecular complexes in a required direction. However, devices known in the prior art do not ensure the formation of highly anisotropic films with reproducible characteristics, which is explained by unavoidable disruption of the oriented molecular structure (defect production) during the film formation. In addition, the technology of film formation using the known devices requires prolonged preliminary work for determining the optimum application conditions for every batch of the initial raw materials.
Attempts at solving the aforementioned problems led to the creation of rather complicated devices, in particular, those containing liquid feed channels of special shapes, additional smoothing elements, etc.
Applicators known in the prior art also include devices of the slot-die coating system type such as the Sony setup (Alabama, USA), Cambridge Shearing System (Linkam Scientific, UK), sliding plate rheometers (FMR-MIT, USA), etc.
Patents depicting various devices of the prior art are U.S. Pat. No. 4,299,789, November 1981, Giesbrecht;
U.S. Pat. No. 4,869,200, September 1989, Euverard; U.S. Pat. No. 6,174,394, 16/2001, Gvon et al.; WO 02/087782, July 2002, Lazarev et al.; and WO 02/056066, July 2002, Lazarev et al.
Despite the existing solutions, problems are still encountered that are related to the need for combining the necessary properties in one device, including high accuracy, simple adjustment, control over the film parameters (in particular, thickness), and the possibility to improve the quality of applied coatings by compensating for substrate unevenness.
The uniqueness of the device according to the present invention is the ability to obtain coatings of large areas at a high rate of application, low consumption of the raw material, and high-precision control over the film thickness and optical parameters (Mueller matrix, alignment, etc.). Additional important advantage of the proposed device is a sufficiently large size of the zone of shear action.